1. Field of the Invention
The invention relates generally to apparatus for converting conventional fluorescent lighting fixtures to use with metric lamping of differing lengths and particularly to extension brackets which facilitate the use of T5 lamping in lighting fixtures intended for use with conventional T12 lamping.
2. Description of the Prior Art
Fluorescent lighting fixtures most commonly employ tubular fluorescent lamps which are of standard designation and which are commonly known as T12 lamps, these lamps typically having nominal lengths of 48 inches, 36 inches and 24 inches. Recently introduced fluorescent lamps having metric dimensions with nominal lengths of 1149 mm, 849 mm, and 549 mm exhibit favorable energy efficiencies and other characteristics which would cause a lighting engineer to consider retrofit of this lamping, known by the standard designation T5, in conventional fluorescent fixtures originally and optimally designed for use with T12 imperial fluorescent lamps. The various lengths of the T5 lamp are considerably shorter than the lengths of the standard T12 lamp sizes. The existing lamp mounting hardware of conventional fluorescent fixtures are not therefore practical for mounting of T5 lamping when considering only the respective lengths of the lamping per se. Since fluorescent lighting fixtures designed for use with T12 lamping are optimized in view of the characteristics of the T12 lamping, a retrofit must necessarily locate T5 or other lamping used in aretrofit situation in locations within the fixtures which provide the best possible photometric performance. Still further, the exigencies of a retrofit situation require accommodation of the differing lengths of T5 or such similar lamping with a minimum number of physical parts which are devoted to this purpose and which therefore must be inventoried in advance of actual assembly to conventional fixtures. The physical parts or articles of manufacture necessary to accomplish the retrofit function must also be inexpensive in addition to being few in number and must accommodate wiring which must pass into an existing lampholder bracket while adequately shielding the wiring from raw metal edges of bracket cutouts and the like.
It has previously been contemplated in the prior art to provide adapter structure for fluorescent lamping which permits fluorescent tubes of differing wattage and shorter length to be installed in lighting fixtures originally configured for use with fluorescent tubes of greater wattage and longer length. Rowe, in U.S. Pat. No. 3,993,386, provides an adapter structure capable of extending the length of a tubular fluorescent lamp. In U.S. Pat. No. 4,758,173, Northrop provides an adapter for extending "tombstone" lamp sockets to permit the use of shorter lamps in fluorescent fixtures. Coldren, in U.S. Pat. No. 5,615,943, describes brackets intended to support fluorescent lamp terminal posts and having individual lamp reflectors extending therebetween and secured to opposing pairs of the brackets for retrofitting existing lamp fixtures with fluorescent lamps and reflectors of a design which differs from those lamps and reflectors for which the fixtures were originally designed. The devices of the prior art do not provide either singly or in combination simple and inexpensive apparatus capable of the retrofit of existing fluorescent lighting fixtures with metric lamping or the like configured as a standard series of differing lengths and which further mount such lamping at an appropriate location within the retrofitted lighting fixtures to provide desirable photometric characteristics.
The present invention provides extension brackets capable of being rapidly attached to standard lampholder brackets of conventional fluorescent lighting fixtures for retrofit of such fixtures, these extension brackets accommodating metric lamping or other lamping which is of generally shorter lengths than conventional tubular T12 fluorescent lamping. The present extension brackets can be configured in two sizes which allow accommodation of the three common sizes of T5 lamping or similar lamping, the extension brackets of the invention attaching by interference fit to standard cutouts of differing configurations such as are variously formed in standard lampholder brackets. The extension brackets of the invention further act to mount conventional lampholders capable of mounting the metric lamping or the like at locations disposed inwardly of the fixtures to not only accommodate the several conventional lengths of such metric lamping but which also locate the metric lamping on a plane no higher than that of the conventional lamping for which the lighting fixtures are originally configured. The extension brackets of the invention can further be installed without effective alteration of existing hardware, thereby allowing rapid removal of the extension brackets and re-equippage of original hardware into the lighting fixtures to allow conversion back to the use of original lamping. The extension brackets of the invention are inexpensive to manufacture and inventory and extraordinarily easy to install in conventional fluorescent lighting fixtures and particularly commercial lighting fixtures utilizing conventional tubular fluorescent lamping.